Several New York City Subway service labels have never been used, but have appeared on rollsigns. DD and FF are covered in the D and F articles. The others are included here.

IRT numbers

Current rollsigns include the following:

• Green 8, 10 and 12 (the same color as the 4, 5 and 6 and the diamond services of the 5 and 6)
• Purple 11 (the same color as the 7 and its diamond service)
• Red 13 (the same color as the 1, 2, 3 and 9)

It is likely that these were assigned arbitrarily, for use if a new service is inaugurated over existing trackage.

IND/BMT letters

P, T, U, X and Y appear on current rollsigns as a black number on a white circle. No current services use this color, so the signs would likely be patched if any of these services were to become permanent. Specifically, T is the planned label for the Second Avenue Line, and would be colored turquoise.

In the 1990s, P was planned for a nonstop between Sutphin Boulevard-JFK Airport (at the 's Jamaica station) and 34th Street-Penn Station , continuing locally to Washington Heights-168th Street , via the BMT Archer Avenue Line , BMT Jamaica Line, Chrystie Street Connection, IND Sixth Avenue Line and IND Eighth Avenue Line (swtiching between the latter at West Fourth Street-Washington Square ). This would have been used during threatened Amtrak strikes that would have prevented LIRR trains from entering New York Penn Station.

P was skipped in the 1960 assignment of letters to services, possibly because of the slang use of the word pee ("go down to track four and take a P", and the fact that the local of the P service would have been PP at the time). T was used for BMT West End Line services, but was quickly eaten up by the post-Chrystie Street expanded B.